Improvement in processes of-building subaqueous tunnels, conduits



H. A. CARSON. Process'of Building Snbnqueous Tunnels, Conduits,

1 and Similar Structures. N0, 22l,66 Patented Nov. 18, 1879.

/ VIIIIIIIIIIIII fittest: Inventor:

MPEFERS. PHOTO-UYHOGRAPHEPL WASHINGTON, D

jNITiEZD warns .PATENT OFFICE.

-HOWARD A. CARSON, OF BOSTON, MASSACHUSETTS.

IMPROVEMENT IN PROCESSES OF'BUILDING SUBAQUEOUS TUNNELS, CO'NDUITS, ANDSIMILAR ST-RUCTURES.

Specification forming part of Letters Patent No. 22 14665, datedNovember 18, 1879 application filed April '14, 1879.

To all whom it may concern:

Be it known that I,v HOWARD ADAMS CAR SON, of Boston, county of Suffolk,and State of Massachusetts, have invented anew and useful Process ofConstructing Tunnels, Conduits, and Similar Structures in ground coveredby water, which process is fully set forth in the followingspecification and accompanying diagrams.

it consists in using a pneumatic caisson in a new and useful "way forbuilding tunnels,

conduits, and similar structures in ground tom of the body of water.

coveredby water. To illustrate precisely this method, a description willbe given of its application to the construction of a conduit of masonryin ground-covered by water.

By pneumaticcaisson is here meant the well-known engineering objectofthat namein brief, a box of timber or metal having four sides .and atop, but openjonthebottom, the sides and top so constructed as to be(when the bottom is sealed) nearly impervious to the passage of air orwater-,the top to be provided with means of ingress and egressthrough'the usual air-locks.

The dimensions of the caisson will depend on the width and depth oftrench. In many cases a height of seven feet, a width four times, and alength five times, as great as the greatest width of the conduit willform convenient dimensions.

At any place where it is desired to begin work, place the pneumaticcaisson so that its longitudinal axis shall be in the same verticalplane as the axis of proposed conduit, and with the lower edge of said.caisson resting on the surface of the earth whichv forms the bot- Afterfilling the caisson with air of such tension as to expel the water, atrench of proper width and any length not greater than that of thecaisson may be excavated, and a conduit built therein. The earth soexcavated, or any part thereof, may be removed from the interior of thecaisson through the air-locks, or in any other way.

I prefer, however, to proceed as follows: First,

excavate a length of trench about one-fifth as long as the caisson,spread the earth in its interior, and build in said trench a shortlength of conduit; continue to excavate short consecutive lengths oftrench, and continue in such excavation the masonry conduit alreadybegun. The earth excavated from the later lengths of trench is placedm'ostly over the conduit previously built.

This process may be illustrated by Figures 1 and 2 on the annexed sheetof diagrams. In Fig. 1, D E is a longitudinal section of a pneumaticcaisson. B B is a longitudinal section of a portion of conduit alreadybuilt.

It is supposed in Fig. 1 that excavation began on the end of caissonnearestD, progressed toward E, and at the time of illustrationexcavation was proceeding in the fourth length of trench, and masonrywork in the third length. These operations are continued until a sectionof conduit is built (such as is shown in Fig. 2) havinga length slightlyless than the length of the caisson, and the surplus earth (equal involume to the volume of the conduit below) is spread.

The bulk-heads F G prevent the surrounding earth from entering theconduit.

Durin g the foregoing operations the successive lengths of trench aretimbered and braced, as may be necessary. The compressed air in thecaisson is preferably kept at no greater tension than that necessary toprevent the entrance of water under the lower edge of the caisson.

Any groundwater which enters the trench is expelled by pumping. For thispurpose a suitable air-engine and pump are placed inside the caisson andconnected with a force-pipe leadin g to the exterior; but preferably apump and engine are placed on a suitable barge or other vessel outsidethe caisson, and have connection with the trench by means of one or moresuction-pipes.

It is to be particularly noticed that the cais son is not sunk throughthe earth during the foregoing operations, but is left with its loweredge only slightly buried in the material forming the bottom of the bodyof water. The caisson is now to be moved forward, keeping itslongitudinal axis over the axis of the proposed conduituntil thecaissons rear end, D, is nearly but not quite in the position formerlyoccupied by its forward end, E, as. shown in Fig. 3. The caisson may befilled with water during this operation and the necessary force for movement and direction applied on the outside. I prefer, however, to raisethe caisson only enough to disengage its lower edge from the mud orother material of the bottom, maintain the airpressure, so as to admitbut little water, and apply the requisite force inside. When the caissonis in its new position the operations performed in its first positionare repeated, and thus the conduit extended.

The bulk-heads may all be allowed to remain in until the whole conduitis completed; or, it" said bulk-heads are provided with suitablemanholes, the second bulk-head, G, may be removed after a third one isput in, and so on.

In the manner described a tunnel, conduit, or any other narrowcontinuous structure may be indefinitely extended in ground covered bywater.

To show the usefulness of this invention, brief mention may be made ofthe principal methods heretofore used for building subaqueoussnbterraneous structures.

The method of drifting has required considerable depth below the bottomof the stream passed under to avoid the danger of bursts of water. Intunnels for roads, going deep is obj ectionable on account of causingsteep grades. If for water, conduits are objectionable on accountofinvolving inverted siphons, in which deposits of silt take place. Evenwhere tunnels under rivers have been located at considerable depthsbelow their bottoms bursts of water have frequently compelled theabandonment of their construction,orsuch construction has been carriedon only at enormous cost.

In the method of cotter-dams of sheet piling the expense increases veryrapidly as depths of water or excavation increase. At depths of fortyfeet this method is usually considered impracticable.

A series of open caissons, each at an interval of a few feet from itsneighbor, sunk by excavating under its edges and simultaneous heavyloading, have been used by me and perhaps by others. In this method itis necessary to join the separate caissons after they are sunka matterof dificulty and expenseand no caisson can be used the second time.Further, the method is limited to small depths.

I am well aware that pneumatic caissons have been repeatedly used forbuilding piers and similar structures. In allsuch cases, however, thecaisson itself has been sunk through the earth where excavation wasresorted to, and left to form a part of the structare. The pneumaticcaisson has never, so far as I am aware, been used tobuild subaqueoussubterraneous structures longer than the caisson itself.

Having thus described my invention, and pointed out its usefulness, whatI claim as new, and desire to secure by Letters Patent, 1s

The method of building tunnels, conduits, and similar structures inground covered by water by a pneumatic caisson, which consists insinking said caisson only so low that its lower edge rests on the bottomof the body of water passed under, and subjecting the air therein tosufficient pressure to prevent the entrance of water under said caissonslower edge, the operation of excavation being" carried on withoutfurther sinking of the caisson, and consecutively placing said caissonso that .its successive positions lap each other, substantially as shownand described.

HOWARD ADAMS CARSON.

Witnesses:

FRANK H. RICHARDSON, ARTHUR F. GRAY.

